New default Git branch name

Git builder now supports pushing and building from the main branch. The behavior for master branch will not change, and will continue to be supported for the foreseeable future. However, please note that in cases when both branches are in context, the main branch will now take priority. For example, for a repository with both main and master branches, pushing all branches with git push fury --all will trigger a main branch build. Still, when you push the branches individually, the builder will continue to consider only the branch being pushed.